Optical matrix switches are useful in optical communication networks wherein large quantities of data are transmitted through optical fibers at high speed. An output optical signal from one of the input optical fibers, each of which is connected to an optical matrix switch, can be supplied to a selective one of output optical fibers also connected to the switch.
Optical switching provides certain advantages over electronic switching techniques; and, oftentimes, optical matrix switches are utilized in electronic transmission lines by converting an electrical signal to an optical signal, passing the signal through the matrix switch and converting the optical signal back to the electronic signal. The advantages of utilizing an optical matrix switch include greatly increased band width and rapid switch configuration rates.
Spanke, U.S. Pat. No. 4,787,692, teaches optical switch networks and design rules for creating the same. The networks comprise a plurality of input and output stages of optical switch elements. Each input optical switch stage is comprised of a plurality of 1.times.2 optical switch elements, and each output stage is comprised of a plurality of 2.times.1 switch elements. The Spanke patent points out that with its invention utilizing such switch network and layout in interconnection, a non-blocking network is achieved having good signal to noise characteristics without crossover and crossthrough limitations as in prior art networks.
Suzuki, U.S. Pat. No. 4,822,124, represents an advancement to the matrix switch of the Spanke patent. As the Suzuki patent points out, with the conventional optical matrix switch, the size thereof is inevitably large in its longitudinal direction. Thus, for example, where the optical switch is provided with four inputs and four outputs to be called a "4.times.4 Optical Matrix Switch", four rows of optical switch elements must be included. Therefore, the longitudinal length cannot be less than a length as much as four times the longitudinal dimension of the optical switch element. In accord with the Suzuki patent, a stage of 2.times.3 optical switch elements is provided in place of two intermediate stages of 1.times.2 and 2.times.1 switch elements to thereby result in an optical switch smaller in the longitudinal direction.
Both prior art patents utilize switching elements based on a Ti--LiNbO.sub.3 substrate. The interconnection of stages of the input and output sections includes optical crossovers and crossthroughs diffused in the same substrate in which the switch elements are formed. The Suzuki patent indicates that, as a result, the substrate on which the four rows of optical switch elements are provided must be large in surface area, thereby substantially increasing fabric casing costs. With 2.times.2 group switch means in the center stage of s switching matrix, the total number of switches otherwise required is decreased, and, correspondingly, the total number of optical crossover and crossthroughs is decreased. Thus, for example, in Spanke, a 4.times.4 matrix switch would be constructed using a stage 2 consisting of eight 1.times.2 switches, a stage 1 adjacent to input ports of four 1.times.2 switches, a stage 3 of eight 2.times.1 switches, and a stage four of four 2.times.1 switches, each connected to an associated output port. With Suzuki, the total of sixteen switches in the intermediate stages 2 and 3 would be replaced by a total of four 2.times.3 switch means, thereby resulting in a matrix switch with a total of twelve switching elements. Again, as with Spanke, the switching elements are Ti--LiNbO.sub.3 substrate based switches.
The present invention takes advantage of certain characteristics of fiber optic transmissions that permit the utilization of optical combining elements, particularly couplers. Couplers are fiber optics light transmitting elements for connecting a plurality of transmission lines and stations. In the present invention, the coupler is a fiber optics transmitting element that connects a plurality of transmission lines from fiber optic switch elements and to an output port. The couplers uniformly couple an optical signal propagating in any one of the plurality of transmission lines from the fiber optics switch elements to a transmission line to the output port. The couplers of the present invention are formed from input and output fiber bundles in the first instance from a single bundle. To this end a plurality of fibers is first provided. As is known, fibers of one standard configuration comprise a 50 micron diameter core and a 125 micron diameter cladding surrounding the core. The fibers are subjected to an etching step or the like, wherein the cladding, on respective intermediate portions, is reduced to minimal thickness, say 2 microns. Intermediate portions are in the order of two to four inches in length with transmission regions on the order of perhaps one-quarter inch between the full diameter and the reduced diameter. The etched fibers are then bonded over at least part of intermediate portions to provide a rigid assembly. Bonding may be accomplished by any convenient technique such as fusing or cementing. The fibers are preferably bonded into a parallel closed packaged triangular or hexagonal configuration. However, no particular symmetry requirement need be imposed. Bonding permits an incoming signal from any one of a number of fibers to be transmitted to an output fiber which is fused thereto. The present invention advantageously utilizes couplers of this description in a fiber optics matrix switch as hereinafter described.
Further, the present invention takes advantage of advances in the fiber optics switching art. As pointed out above, both the Spanke and Suzuki patents utilize switching elements based on a Ti--LiNbO.sub.3 substrate. As both patents point out, with such switching elements, the longitudinal length of the matrix switch becomes critical. However, advances in the fiber optic switching art make possible the providing of discrete fiber optic switches which may be combined to form matrix switches wherein the longitudinal length is not of the criticality of matrix switches utilizing the substrate switches of the prior art. Switching elements useful in the matrix switches of the present invention are those taught by Gutterman, et al., U.S. Pat. No. 4,854,660, and Kokoshvill, U.S. pending application, Ser. No. 053,220, entitled "Fiber Optic Bypass Switch", filed on May 13, 1987, having European priority No. EP 0 299 604 Al. The switch elements of the matrix switches of the present invention include an imaging system having a symmetry such as a spherical reflector. The switch also includes a group of optical fiber end faces including a first optical fiber end face via which light is transmitted to the imaging system and at least second and third fiber optic end faces. A translation mechanism is provided for linearly translating the imaging system and the fiber end face group relative to one another between two positions. In a first position, the first and second fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the second fiber. In a second position, the first and third fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the third fiber. Thus, it is possible to switch the light from the first fiber into the second fiber or into the third fiber depending on the position of the linear translation mechanism.